Diseases involving inflammation are characterized by the influx of certain cell types and mediators, the presence of which can lead to tissue damage and sometimes death. Diseases involving inflammation are particularly harmful when they afflict the respiratory system, resulting in obstructed breathing, hypoxemia, hyperapnia and lung tissue damage. Obstructive diseases of the airways are characterized by airflow limitation (i.e., airflow obstruction or narrowing) due to constriction of airway smooth muscle, edema and hypersecretion of mucus leading to increased work in breathing, dyspnea, hypoxemia and hypercapnia.
A variety of inflammatory agents can provoke airflow limitation including allergens, cold air, exercise, infections and air pollution. In particular, allergens and other agents in allergic or sensitized mammals (i.e., antigens and haptens) cause the release of inflammatory mediators that recruit cells involved in inflammation. Such cells include lymphocytes, eosinophils, mast cells, basophils, neutrophils, macrophages, monocytes, fibroblasts and platelets. Inflammation results in airway hyperresponsiveness (AHR). A variety of studies have linked the degree, severity and timing of the inflammatory process with the degree of airway hyperresponsiveness. Thus, a common consequence of inflammation is airway hyperresponsiveness.
Currently, therapy for treatment of inflammatory diseases involving AHR, such as moderate to severe asthma and chronic obstructive pulmonary disease, predominantly involves the use of glucocorticosteroids and other anti-inflammatory agents. These agents, however, have the potential of serious side effect, including, but not limited to, increased susceptibility to infection, liver toxicity, drug-induced lung disease, and bone marrow suppression. Thus, such drugs are limited in their clinical use for the treatment of lung diseases associated with airway hyperresponsiveness. The use of anti-inflammatory and symptomatic relief reagents is a serious problem because of their side effects or their failure to attack the underlying cause of an inflammatory response. There is a continuing requirement for less harmful and more effective reagents for treating inflammation. Thus, there remains a need for processes using reagents with lower side effect profiles, less toxicity and more specificity for the underlying cause of AHR.
Airway hyperresponsiveness (AHR) is the result of complex pathophysiological changes in the airway. A variety of studies have linked the degree, severity and timing of the inflammatory process with the degree of airway hyperresponsiveness. However, the mechanisms leading to AHR are still poorly understood and can be attributed to both immune-dependent and immune-independent mechanisms. Essentially all of the T cell-mediated effects described so far are in the former category. However, T cells from hyperresponsive mice can increase baseline airway tone in hyporesponsive mice after cell transfer. Because of their constitutive presence in the normal lung, γδ T cells have been investigated with regard to their potential role in airway responses.
γδ T cells have been observed to proliferate and produce cytokines in many diseases. In addition, studies in animal models have provided evidence that these cells contribute to host resistance against infections (Hiromatsu et al., 1992, J. Exp. Med. 175:49), and that they can influence inflammation (Fu et al., 1994, J. Immunol. 153:3101), epithelial regeneration (Boismenu et al., 1994, Science 266:1253), and mucosal tolerance to antigens (Fujihashi et al., 1992, J. Exp. Med. 175:695; McMenamin et al., 1994, supra). Investigators are still determining what stimuli trigger γδ T cell reactivity, and to what extent γδ T cell activating stimuli differ from those of αβ T cells and B lymphocytes. It is known that γδ T cells respond during bacterial and viral infections, although they have not been readily linked to antigen-specific adaptive immunity.
A number of studies have investigated the presence and role of γδ T cells in diseases of the airways. Pawankar et al. noted the mucosal changes at the site of allergic inflammation in patients with perennial allergic rhinitis and chronic infective rhinitis includes an oligoclonal expansion and activation of Vγ1/Vδ+ T cells (Pawankar and Ra, 1996, J. Allergy Clin. Immunol. 98:S248-62). Molfino et al. showed that much of the γδ T cell population found in broncho alveolar lavage (BAL) fluid in humans derives from clonally expanded T cells (Molfino et al., 1996, Clin. Exp. Iminunol. 104:144-153). Spinozzi et al., measuring γδ T cells in the BAL fluid from patients with asthma, concluded that allergen-specific, steroid-sensitive γδ T cells may be one of the cellular components involved in the airway inflammation that characterizes allergic bronchial asthma (Spinozzi et al., 1996, Ann. Intern. Med. 124:223-227 and 1995, Mol. Med. 1:821-826).
Moreover, it has been noted that in patients with respiratory conditions including Bordetella pertussin infection (whooping cough) and asthma, circulating γδ T cells are decreased. It has been suggested that the reason for this decrease is the dispatch of γδ T cells to the site of inflammation in the lung. (Bertotto et al., 1997, Acta Paediatr. 86:114-115; Schauer et al., 1991, Clin. Exp. Immunol. 86:440-443; Krejsek et al., 1998, Allergy 53;73-77).
Many of the studies directed to γδ T cells and airway diseases have directly suggested that γδ T cells are proinflammatory, promoting acute airway sensitization, increases in cytokine levels suggested to be involved in allergic inflammation, regulation of allergic αβ T-cell and allergen specific B-cell responses, and/or allergen-induced eosinophilia and IgE responses (e.g., McMenamin et al., 1994, Science 265:1869-1871; Zuany-Amorim et al., 1998, supra; Schramm et al., 2000, Am. J. Respir. Cell Mol. Biol. 22:218-225; Schramm et al., 1999, International Conference of the American Thoracic Society; vol. 159:A255 (American Journal of Respiratory and Critical Care Medicine, San Diego, Calif.)). Some investigators, alternatively, have concluded that γδ T cells do not play a significant role in airway allergic inflammation. For example, Chen et al. noted, similar to other investigators discussed above, that allergic asthmatics have reduced γδ T cells in the peripheral blood. However, Chen et al. concluded that no significant correlation existed between the levels of γδ T cells and IgE present in the peripheral blood (Chen et al., 1996, Clin. Exp. Iminunol. 26:295-302). Although allergic asthmatics have reduced γδ T cells with reciprocally elevated eosinophil numbers in the peripheral blood, Chen et al. asserted that this does not indicate that the reduction of γδ T cells correlates with the predominance of eosinophilia or IgE levels in diseased populations. Jaffar et al. described a role for αβ, but not γδ, T cells in allergen-induced Th2 cytokine production from asthmatic bronchial tissue (Jaffar et al., 1999, J. Immunol. 163:6283-6291). Fajac et al., 1997, Eur. Resp. J 10:633-638 investigated the role of heat shock proteins and γδ T cells in patients with mild atopic asthma, and concluded that neither heat shock proteins nor γδ T cells play an important role in inflammatory and immune responses in mild asthma.
Therefore, prior to the present invention, those of skill in the art either considered γδ T cells to play an insignificant role, if any, in diseases of the airways, or believed that γδ T cells were proinflammatory cells which contributed to the development of acute airway hyperresponsiveness and other events associated with inflammation.